Method of producing luminescent screens for cathode ray tubes



Oct. 7, 1958 A. Y. BENTLEY 2,

METHOD OF PRODUCING LUMINESCENT SCREENS FOR CATHODE RAY TUBES Filed Dec. 3, 1953 COMPONENT "A" L06 BRIGHTNESS confiols/E/vr'a" I 1 I 1 H 12 L06 TIME f3 LOG BRIGHTNESS 1 2 LOG'TIME---4 *3 Fig. 2

INVENTOR. ALFRED YOUNG BENTLEY A TTORNEYS United States Patent METHOD OF PRODUCING LUlVIlNESCENT SCREENS FOR CATHODE RAY TUBES Alfred Young Bentley, Packanack Lalre, N. J., assignor to Allen B. Du Mont Laboratories, Inc., Clifton, N. 1., a corporation of Delaware Application December 3, 1953, Serial No. 395,873

Claims. (Cl. 11733.5)

This invention relates to preparation of a phosphor material for cathode ray tube screens and to a composition thereof useful in the formation of screens, the material being characterized by its luminescent characteristics which consist of modified after-glow, so that there is a substantial long period of after-glow, thus rendering possible examination of information'presented on a cathode ray tube screen for a substantial period after excitation has been discontinued.

For many purposes it is desirable that a cathode ray tube screen have a luminescent characteristic in which the light given off will be proportional to the excitation, and which further will have an extended period of light decay so that the presentation of information on the screen over an extended period of time can take place. For example, in certain radar applications it is frequently necessary to display information in the after-glow which is applied to the viewing area of the screen at more than one rate. The scanning of a screen in one case may be such as to display on a map certain amounts of information in 3 seconds. In another instance, the complete map is presented over a period of seconds. In using common screen materials, those which are appropriate for the first case are not satisfactory for the second, because they do not have a suhiciently long decay time. Conversely, a screen suitable for a long period of slow presentation of information is not suitable for the rapid presentation of information because of confusion caused by the excessively long decay time.

It is accordingly a fundamental object of my invention to provide a screen component which has a dual decay characteristic so that for a brief interval of time following excitation, decay will be rapid, following which it will proceed slowly to extinguishment.

Other objects and advantages of the invention will in part be obvious and in part appear hereinafter.

The invention accordingly is based upon the formation of a screen characterized by having two distinct rates of decay of after-glow therein, the ingredients of the screen being those which correspond to the empirical formula K MgF plus a material formed by mixing potassium fluoride and magnesium fluoride in a molar excess with activator amounts of manganese fluoride or zinc sulfate.

In the drawing, Figures I and II are graphical representations in empirical form of the brightness of the luminescence from the composition when measured against time following excitation.

For the preparation of the materials, the first ingredient corresponding to the empirical composition K MgF is prepared as follows:

In an appropriate container the following ingredients are mixed:

that form is ready for use.

2 and suflicient aqueous hydrogen fluoride of a concentration of about 20 percent by weight is added so that the material can be stirred into a uniform, moderately thick paste in which the potassium fluoride is dissolved. The paste is then heated to dryness at about C. and the resulting cake is milled in water for a period of several hours, which may be as long as 15 hours. It is then filtered and dried at about 100 C., and fired in an appropriate crucible, such as platinum, at 1450 for an hour. To assure thorough intimate blending of the potassium fluoride and magnesium fluoride, it can be reground in the aqueous medium for a period of about an hour, filtered, dried-and refired at about 1400 F. for an hour. Following the reduction to a degree of fineness suflicient to pass a 325- mesh sieve, it is ready for use.

The proportion of manganese fluoride used in the composition represents an approximate optimum for luminescent efficiency but ratios thereof from 0. 2 to 1 percent by weight (.003-.014 mol.) may be used to give phosphors having essentially the same characteristics. Similarly, the proportions for the potassium fluoride to magnesium fluoride ratio are essentially 2 to 1 on a molar basis and this represents an optimum ratio for development of the desired property. Deviations from the optimum ratio to 22:1 to 1.821 maintain substantially the desired light characteristics in this ingredient.

For the second ingredient, which consists of potassium fluoride-magnesium fluoride composition containing the indicated substantial excess of magnesium fluoride, the composition may be prepared substantially as follows:

The following amounts of potassium fluoride and magnesium fluoride and manganese fluoride are mixed in an appropriate container:

Percent Sufficient aqueous hydrogen fluoride solution, for example, a concentration of about 20 percent by weight, is stirred into the material to form a uniform paste and the material is then dried at about 100 0., following which the mixture is transferred to a pebble mill where about 6 grams of anhydrous zinc sulfate is added. A suflicient amount of water is added to form a slurry, and this is milled in a ball-mill for a period of 1 to 15 hours, filtered, and then dried at 100 C. Following this it is fired in platinum for a period of about 1 hour at 1500 F. The material is then ball-milled in an aqueous medium for an hour with suficient water simply to moisten it to form a thick slurry, filtered, dried and refired at 1450 F. for about an hour. It is then ground to a degree of fineness sufficient to pass a 325 mesh sieve and when reduced to These proportions are appropriate for a composition corresponding to 1.1 mole of potassium fluoride to 1 mole of magnesium fluoride with trace amounts of manganese and zinc, but the proportions thereof may be varied to as much as a tenfold molar excess of the magnesium fluoride. Within this range a series of solid solutions of potassium fluoride-magnesium fluoride compositions are obtained having essentially the light characteristics desired, which are bright fluorescence with a low end flash.

These two potassium fluoride-magnesium fluoride compositions when blended together in their finely divided form simply by mixing, produce a screen having a high intensity response to excitation with the dual decay characteristic described in the accompanying diagrams.

Depending upon the exact degree of variation in the dual decay characteristic desired in the final cathode ray tube screen, the two ingredients may be blended in a ratio of one part by weight of one to ten parts of the other to ten parts of the first to one part of the second. Their blending and proportions in which they are blended is dependent upon the actual duration of the two sections of the decay characteristic desired and generally it will be found most desirable to utilize blends in which they are present in substantially equal parts by weight.

' In the diagrams accompanying this instant invention, two graphs are presented showing a plot of brightness against time when the screens are made up of about equal parts by weight of the two components indicated. That is, the first ingredient, which has the rapid decay time, will decay from maximum brightness to substantially Zero in the interval up to t To achieve the objects of the invention, it is preferred that the materials be blended in a proportion such that a useful period in the interval t to 1 is obtained as well as in the period t to t is shown in Figure 2. During the period t t the light intensity of the two ingredients of the screen and decay component A is of a maximum intensity for a brief period through a break in the curved course at the point identified as t Within either of the intervals useful information can be presented on the cathode ray tube screen. Variation of the stoichiometric relationship of the two components may be employed so that the break in the curve may be made to occur at any of several points between t and t By forming a screen having this empirical form of decay characteristic with separately identifiable periods of time delay in its decay, the final screen formed therewith is rendered useful for the rapid presentation of information as well as slow presentation of information on the cathode ray tube screen.

Though the invention has been described in connection with only a single embodiment, it is to be understood that variations thereof may be practiced without departing from the spirit or scope thereof.

What is claimed is:

.1. A process for producing a composite phosphor with a selective dual decay characteristic useful for cathode ray tubes comprising the steps of: mixing a first ingredient consisting of potassium fluoride and magnesium fluoride in substantially the molar ratio of 2.2:1 to 1.8:1 with activator amounts of manganese fluoride ranging from .003 to .014 mol, firing said first ingredient at an elevated temperature, mixing a second ingredient consisting of potassium fluoride and magnesium fluoride in substantially the molar ratio of about 1.1:1 to 1:10 with activator amounts of about .001 mol of manganese fluoride and about .04 mol of zinc sulphate, firing said second ingredient at an elevated temperature; and blending said first and second ingredients in amounts ranging from one part of said first ingredient to ten parts of said second ingredient, to ten parts of said first ingredient to one part of said second ingredient, said composite phosphor being characterized by its selective dual decay characteristic.

2. A composite phosphor produced in accordance with claim 1 in which said first and second ingredients are present in substantially equal parts.

3. A method of producing a cathode ray tube having a selective dual decay characteristic viewing screen therein, said screen being formed by the steps of: mixing a first ingredient consisting of potassium fluoride and magnesium fluoride in substantially the molar ratio of 2.2:1 to 1.8:1 with activator amounts of manganese fluoride ranging from about .003 to about .014 mol, firing said first ingredient at an elevated temperature; mixing a second ingredient consisting of potassium fluoride in substantially the molar ratio of about 1.1:1 to 1:10 in the presence of activators in the amounts of about .001 mol of manganese in the presence of about .04 mol of zinc sulphate, firing said second ingredient at an elevated temperature, blending said first and second ingredients in amounts ranging from one part of said first ingredient to ten parts of said second ingredient, to ten parts of the first to one part of said second ingredient, and depositing said blend of first and second ingredients on a surface of said cathode ray tube to form a viewing screen therein characterized by its selective dual decay light characteristic.

4. The method of claim 3 in which the mixture of first and second ingredients is ground together and reduced to a high degree of subdivision.

5. The method of claim 3 in which said first and second ingredients are present in substantially equal parts.

References Cited in the file of this patent UNITED STATES PATENTS Leverenz Oct. 12, 1948 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 2,855,325

I October '7, 1958 Alfred Young Bentley It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line 24, claim 3, after "manganese" insert fluoride Signed and sealed this 30th day of December 1958,

(SEAL) Attest:

KARL I-Io AXLINE Commissioner of Patents 

3. A METHOD OF PRODUCING A CATHODE RAY TUBE HAVING A SELECTIVE DUAL DECAY CHARACTERISTIC VIEWING SCREEN THEREIN, SAID SCREEN BEING FORMED BY THE STEPS OF: MIXING A FIRST INGREDIENT CONSISTING OF POTASSIUM FLUORIDE AND MAGNESIUM FLUORIDE IN SUBSTANTIALLY THE MOLAR RATIO OF 2.2:1 TO 1.8:1 WITH ACTIVATOR AMOUNTS OF MANGANESE FLUORIDE RANGING FROM ABOUT .003 TO ABOUT .014 MOL, FIRING SAID FIRST INGREDIENT AT AN ELEVATED TEMPERATURE; MIXING A SECOND INGREDIENT CONSISTING OF POTASSIUM FLUORIDE IN SUBSTANTIALLY THE MOLAR RATIO OF ABOUT 1.1:1 TO 1:10 IN THE PRESENCE OF ACTIVATORS IN THE AMOUNTS OF ABOUT .001 MOL OF MANGANESE IN THE PRESENCE OF ABOUT .04 MOL OF ZINC SULPHATE, FIRING SAID SECOND INGREDIENT AT AN ELEVATED TEMPERATURE, BLENDING SAID FIRST AND SECOND INGREDIENTS IN AMOUNTS RANGING FROM ONE PART OF SAID FIRST INGREDIENT TO TEN PARTS OF SAID SECOND INGREDIENT, AND DEPOSITING SAID BLEND OF FIRST SAID SECOND INGREDIENTS ON A SURFACE OF SAID CATHODE RAY AND SECOND INGREDIENTS ON A SURFACE OF SAID CATHODE RAY TUBE TO FORM A VIEWING SCREEN THEREIN CHARACTERIZED BY ITS SELECTIVE DUAL DELAY LIGHT CHARACTEISTIC. 